This invention relates to an improvement in the transfer of particulate solids through a conduit from one pressure zone to another pressure zone. The invention finds application in the chemical processing industry where it is desired to transfer granular solids through a pipe from a first vessel held at a first pressure to a second vessel held at a second pressure while maintaining the pressure in each vessel. The transfer of such solids is required during the processing of coal into gas and oil which results in the production of granular particles of char or coke which are transferred through a pipe connecting vessels held at different pressures.
Double gate valves and star feeders are commonly used in pipes communicating with vessels maintained at different pressures where it is desired to maintain a separation between the two pressure zones but allow for the flow of particulate solids between the vessels. The presence of particulate solids in the communicating pipe may also be used as a seal to separate the two pressure zones and when so used the communicating pipe is referred to as a seal leg or a seal pipe.
Seal legs are of a substantial length because it has been observed that solids will now flow through the pipe (the seal leg) at the required flow rate if the pipe is too short. Consequently, if the particulate solids are to be used as a pressure seal in the pipe, the pipe is relatively long. For example, a seal leg length of 150 feet would be required to pass 30,500 pounds per hour of a 0.0041 inch diameter solids having a bulk density of 149.5 pounds per cubic foot and an angle of repose of 45.degree. from an upper pressure zone at atmospheric pressure to a lower pressure zone at 30 psig through a 4 inch interior diameter seal pipe.
Seal legs of such length are objectionable, however, because they end to promote plugging within the pipe and they may be in violation of local building codes if they cause the height of the structure with which they are associated to be greater than permitted by such codes.